1. Field of Invention
The present invention relates in general to reciprocating internal combustion engines of a variable compression ratio type that is capable of varying a compression ratio under operation thereof and more particularly to the reciprocating internal combustion engines of a multi-link type wherein each piston is connected to a crankshaft through a plurality of links. More specifically, the present invention is concerned with a piston control mechanism of such internal combustion engines.
2. Description of Related Art
In the field of reciprocating internal combustion engines, there has been proposed a variable compression ratio type that is capable of varying a compression ratio of the engine in accordance with operation condition of the same. One of such engines is shown in Laid-Open Japanese Patent Application (Tokkai) 2000-73804. The engine of the publication employs a piston control mechanism wherein each piston is connected to a crankshaft through a plurality of links.
For ease of understanding of the present invention, the piston control mechanism of the publication will be briefly described with reference to FIG. 12 of the accompanying drawings.
In the drawing, denoted by numeral 101 is a crankshaft having crank pins 102. To each crank pin 102, there is pivotally connected a lower link (floating lever) 103 at a middle portion thereof. To one end of lower link 103, there is pivotally connected a lower end of an upper link 106 through a first connecting pin 110. An upper end of the upper link 106 is pivotally connected to a piston 104 through a piston pin 105. To the other end of lower link 103, there is pivotally connected a lower end of a control link 107 through a second connecting pin 111. An upper end of control link 107 is pivotally connected to an eccentric pin 109 of a control crankshaft 108. More specifically, the lower and upper ends of control link 107 are formed with respective cylindrical bearing bores which pivotally receive second connecting pin 111 and eccentric pin 109 respectively. Under operation of the engine, control crankshaft 108 is turned in accordance with operation condition of the engine, causing control link 107 to vary and set pivoting movement of lower link 103 thereby varying or setting a stroke of the piston 104. With this operation, the compression ratio of the engine is varied in accordance with the engine operation condition.
In the piston control mechanism as mentioned hereinabove, based on both an upward inertial load applied to piston 104 when piston 104 moves upward and a downward load applied to the same when combustion takes place, a certain load is inevitably applied to control link 107 through upper link 106 and lower link 103. In control links like the control link 107 of which both ends are formed with cylindrical bearing bores, it is known that an elastic deformation appearing on control link 107 when a tensile load is applied thereto is greater than that appearing when a compression load is applied thereto. That is, variation of effective length of control link 107 in case of receiving the tensile load is larger than that in case of receiving the compression load. That is, in case of the compression load, only a shaft portion proper of control link 107 defined between the two cylindrical bearing bores is subjected to an elastic deformation, while, in case of tensile load, the entire length of control link 107 including the two thinner cylindrical bearing bores is subjected to the elastic deformation inducing the increase in elastic deformation degree.
When piston 104 comes up to a top dead center (TDC) on exhaust stroke, upward inertial load of piston 104 brings the crown of the same into a position closest to intake and exhaust valves. Furthermore, when, due to valve overlapping or the like, intake and exhaust valves are still open partially at such top dead center (TDC), the piston crown becomes much closer to the intake and exhaust valves. Thus, when, with piston 104 taking the top dead center (TDC) on exhaust stroke, a certain tensile load is applied to control link 107 based on the upward inertial load of piston 104, the elastic deformation of control link 107 becomes remarkable causing piston 104 to be displaced from a proper position, which tends to deteriorate engine performance. Furthermore, if the displacement of piston 104 becomes remarkably large, undesirable interference between piston 104 and intake and exhaust valves may occur.
Accordingly, an object of the present invention is to provide a piston control mechanism of reciprocating internal combustion engine, which is free of the above-mentioned undesired piston displacement.
Another object of the present invention is to provide a piston control mechanism of reciprocating internal combustion engine of variable compression ratio type, which can assuredly avoid interference between a piston and intake and exhaust valves without sacrificing engine performance, that is, without narrowing a range in which the engine compression ratio is variable.
Still another object of the present invention is to provide a piston control mechanism of reciprocating internal combustion engine of variable compression ratio type, which is compact in size and exhibits a high cost performance.
According to a first aspect of the present invention, there is provided a piston control mechanism of an internal combustion engine, the engine including a piston slidably disposed in a piston cylinder and a crankshaft converting a reciprocation movement of the piston to a rotation movement, the piston control mechanism comprising a lower link rotatably disposed on a crank pin of the crankshaft; an upper link having one end pivotally connected to the lower link and the other end pivotally connected to the piston; a control link having one end pivotally connected to the lower link; and a position changing mechanism which changes a supporting axis about which the other end of the control link turns, wherein when the piston comes up to a top dead center, a compression load is applied to the control link in an axial direction of the control link in accordance with an upward inertial load of the piston.
According to a second aspect of the present invention, there is provided a piston control mechanism of an internal combustion engine, the engine including a piston slidably disposed in a piston cylinder and a crankshaft converting a reciprocation movement of the piston to a rotation movement, the piston control mechanism comprising a lower link rotatably disposed on a crank pin of the crankshaft; an upper link having one end pivotally connected to the lower link and the other end pivotally connected to the piston; a control link having one end pivotally connected to the lower link; and a position changing mechanism including a control crankshaft which extends in parallel with the crankshaft and rotates about a given axis, the control crankshaft including a main shaft portion which is rotatable about the given axis and an eccentric pin which is radially raised from the main shaft portion, the eccentric pin being received in a cylindrical bearing bore formed in the other end of the control link, wherein when the piston comes up to a top dead center, a rotation direction of an upper link center line relative to a first direction line is equal to a rotation direction of a control link center line relative to a second direction line, the upper link center line being an imaginary line which perpendicularly crosses both a first pivot axis between the piston and the upper link and a second pivot axis between the upper link and the lower link, the control link center line being an imaginary line which perpendicularly crosses both a third pivot axis between the lower link and the control link and the supporting axis, the first direction line being an imaginary line which perpendicularly crosses both the second pivot axis and a center axis of the crank pin, and the second direction line being an imaginary line which perpendicularly crosses both the third pivot axis and the center axis of the crank pin.